The brain is the top sex organ, so stimulate it. Ask her to imagine how much fun and exciting it would be to have hot sex with a stranger, engauge her in fantasy sex talk, encourage her to let her naughty side come out to play. have her wear revealing clothing when you go and point out the attention she receives and tell her to imagine the guys she finds attractive seducing her, complement her efforts to be sexy, assure her havening sex with other men will be okay with you, you won't be jealous, just the opposite as it will turn you on, Tell her that she should not have any guilt as she is doing what you want her to do. Ask her to remember how exciting her first date was and tell her that she can get that excitement back when she hooks up with another man and has sex. Keep her curious about what it's like to have sex with another man. Tell her she deserves the extra attention and sexual excitement that comes with being with another man will give her. Give her time to let her imagine run wild and accept the idea. Don't pressure her but from time to time bring up the idea, during sex when she's excited might be effective time to suggest it again. Just keep her thinking about it when she in a receptive mood. When she starts asking how its to be done, you are moving forward but don't rush it, it takes time and reassurance that she isn't going to hurt you or your relationship but improve it as sex becomes hotter and more engaging due to the efforts on her part. Show her positive reactions from other women who have already done this. Encourage her to put herself out there and enjoy the rewards for the both of you.